Neuronal galanin is widely distributed in the chicken respiratory tract and coexists with multiple neuropeptides.

The mammalian airways are known to be richly innervated by several types of peptide-containing nerve fibers. Galanin-containing fibers are, however, comparatively few. The results of the present immunocytochemical study indicate that the chicken airways receive a notably dense supply of galanin-storing fibers. Other major neuropeptides were neuropeptide Y, vasoactive intestinal peptide and substance P. Nerve fibers containing these peptides were distributed in the trachea, main bronchi, and the lungs. Minor nerve fiber populations contained calcitonin gene-related peptide, enkephalin and gastrin-releasing peptide. In the trachea and main bronchi the majority of peptide-containing nerve fibers was distributed beneath and sometimes also within the epithelium; fibers were fewer in the lamina propria. In the lungs they occurred both in association with the epithelium of small bronchi and in the septa. Adrenergic nerves (using tyrosine hydroxylase as marker) were predominantly distributed in the lamina propria among bundles of smooth muscle and blood vessels. In the nerve fibers associated with the epithelium and in nerve cell bodies in local ganglia of the tracheal wall, galanin was found to coexist with several other neuropeptides (neuropeptide Y, vasoactive intestinal peptide and substance P) suggesting co-expression of multiple neuropeptide genes in the same population of neurons.